As integrated circuit (IC) geometries and micro-electro mechanical systems (MEMS) continue to get smaller, the need for reliable high density packaging solutions increases. A promising solution providing reliable packaging for chips of continually decreasing size is wafer level packaging (WLP). WLP is a packaging method in which packaging is formed at the wafer level in an IC foundry or other processing location. WLP allows for testing and burn-in to be performed on a wafer prior to the dicing of the wafer into individual chips.
In certain WLP methods, small cavities or enclosures of an IC or MEMS package may be filled with a fluid. In many such applications, fluid filling of a WLP may need to be performed in such a way as to prevent bubbles or gaseous pockets from forming in the fluid filled cavities. Fluid filling small cavities like those in WLPs without trapping bubbles inside the cavities is a challenge, due to the different relative strengths of various forces at the micro-scale. One such force is surface tension at the surface of a liquid. On the macro scale, surface tension is relatively weak. However, on the micro-scale surface tension may be very strong and even dominate other typically strong forces.
As physical dimensions shrink to the micro-scale, the strength of surface tension on fluids continues to increase relative to other mechanical forces. Surface tension of fluids at the micro level may prevent fluids from flowing into cavities under normal conditions during the fluid filling of wafer level cavities. Traditional equipment used to overcome these surface tensions are expensive and require a large lead time to produce. Furthermore, traditional equipment often experiences cross-contamination when switching between fill fluids. Additionally, traditional fluid filling equipment may not be energy or fill fluid efficient when applied to wafer level filling, further increasing operating costs.